The development of microporous foams has been the subject of substantial commercial interest. The properties of these foams can be varied to advantage for applications ranging from thermal, acoustic, electrical, and mechanical (e.g., for cushioning) insulators, absorbent materials, filters, carriers for inks, dyes, lubricants, and lotions, making items buoyant, and the like. References describing such uses and properties of foams include Oertel, G. "Polyurethane Handbook" Hanser Publishers, Munich, 1985, and Gibson, L. J.; Ashby, M. F. "Cellular Solids. Structure and Properties" Pergamon Press, Oxford, 1988. The term "insulator" refers to any material which reduces the transfer of energy from one location to another. The term "absorbent" refers to materials which imbibe and hold or distribute fluids, usually liquids, often water, an example being a sponge. The term "filter" refers to materials which pass a fluid, either gas or liquid, while retaing impurities within the material. The term "carrier" refers to materials which hold a second substance, usually a liquid, until such time as the second substance is needed for a separate purpose at which point it is expressed by pressure.
Many of these applications require foam which resists burning. Many building codes, for example, include restrictions on the flammability of materials including foam insulation. Similar restrictions can apply to insulation used in clothing or protective apparel. However, most plastic materials, including foams, burn readily. In order to provide for the safe use of such materials in these applications, various approaches to retarding the flammability of organic polymers have been developed. These approaches are discussed generally by John Lyons in the book "The Chemistry and Uses of Fire Retardants", Robert Krieger Publishing Co., Malabar, FL, 1987. These approaches are diverse but generally comprise inclusion of compounds containing certain heteroatoms--generally chlorine, bromine, phosphorus, boron, and/or antimony in the organic polymer. These compounds include small molecules, oligomers, and polymers. Inorganic additives are also used, including antimony trioxide and related salts as well as salts containing borate or phosphate anions. The science of flame retardancy as applied to conventional plastic materials is reasonably well developed, as discussed in the cited text.
Additional properties of the foam are often required depending on the intended use. These generally include one or more of the following: (1) low density, (2) flexibility, (3) strength (compressive and tensile), (4) openness, and (5) control of morphology. Low density foams are more efficient since most uses require a certain volume. A low density foam will impose less mass to meet this objective. Flexible foams are typically generated by maintaining a relatively low glass transition temperature ("Tg") of the foam. Strength is a parameter which can be challenging to achieve concurrent with lower Tg and/or lower density. Strength (independent of density) is most effectively generated by including crosslinking agents which link the polymeric chains of the foam together in a fashion which confers a degree of resistance to deformation and the ability to recover from deformation, e.g., elasticity. Openness and morphology are controlled principally by the method of foam formation and curing.
One of the benefits of high internal phase emulsions foams or HIPEs is that the foams can be tailored to have one or more of the desired properties discussed above. The conference of flame retardancy to HIPE foams is not straightforward. However, it would be desirable to be able to make an open-celled, high surface area HIPE foam which is flame retardant and which has one or more of the following properties: (1) the lowest density consistent with the other requirements imposed on the foam; (2) flexibility; (3) strength; (4) a generally open-celled structure; and (5) the ability to be manufactured so as to control the size of cells produced within the foam.